During the current year I studied the distribution and redistribution of membrane particles and gap junctions visualized by freeze-fracture of normal and virally transformed Balb/c and Swiss 3T3 fibroblasts in culture. Contrary to other reports, no apparent differences are found in the native distribution of membrane particles in normal and transformed cells. This work, taken with previous evidence, also implies independence of Con A receptors and membrane particles in the cells. In erythrocyte membranes, however, we found that Con A receptors were exclusively associated to the membrane particles. The concept of a "permeaphore" was proposed as a unit with a topology and structure adequate to the transmembrane passage of ions and hydrophylic molecules. In pathogenic strains of Entamoeba histolytica study is made of the relationship cell structure-membrane structure which leads to the proposal of the concepts of integral and peripheral membrane fluidity.